Question 247253 in Json Question posted in
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Mapping JSON Result to an Enum in Swift

I have the following response from JSON service:

[
    {
        "id": 1,
        "name": "Student"
    },
    {
        "id": 2,
        "name": "Faculty"
    }
]

And I want to map it to an enum:

enum Role: Int, Codable, Identifiable {
    case student
    case faculty
    
    var id: Int {
        rawValue
    }
}

But I am having trouble mapping since the array in JSON contains dictionaries.

Tags:

2

Answers


  1. 0

    Your objects have 2 member : id which is an Int and name which is a string that you want to use an enum for it :

    struct Role: Codable, Identifiable {
    enum RoleName: String, Codable {
        case student = "Student"
        case faculty = "Faculty"
    }
    var name: RoleName
    var id: Int
}

    example for decoding :

    let json = """
[
    {
        "id": 1,
        "name": "Student"
    },
    {
        "id": 2,
        "name": "Faculty"
    }
]
"""

var roles = [Roles]()
if let data = json.data(using: .utf8) {
   roles = try? JSONDecoder().decode([Role].self, from: data)
}

    Edit: corrected type of name + coding key for enum

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  2. 0

    What you need is a custom encoder and decoder. Another issue in your code is that you are not specifying the integer value of your enumeration cases which should start with 1 (if you don’t specify it will start with zero). So your enumeration should look like this:

    enum Role: Int, Codable, Identifiable {
    case student = 1, faculty
    var id: RawValue { rawValue }
    private enum CodingKeys: String, CodingKey {
        case id, name
    }
}

    Then you can create a custom decoder:

    extension Role {
    public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let id = try container.decode(Int.self, forKey: .id)
        let name = try container.decode(String.self, forKey: .name)
        switch (id, name) {
        case (1, "Student"):
            self = .student
        case (2, "Faculty"):
            self = .faculty
        default:
            throw DecodingError.dataCorrupted(
                .init(
                    codingPath: decoder.codingPath,
                    debugDescription: "Invalid Role data"
                )
            )
        }
    }
}

    And if you need to encode it as well a custom encoder:

    extension Role {
    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        switch self {
        case .student:
            try container.encode("Student", forKey: .name)
        case .faculty:
            try container.encode("Faculty", forKey: .name)
        }
    }
}

    Playground testing:

    let jsonData = Data(#"[{"id":1,"name":"Student"},{"id":2,"name":"Faculty"}]"#.utf8)
let roles: [Role] = [
    .init(rawValue: 1)!,
    .init(rawValue: 2)!
]
let encodedRoles = try JSONEncoder().encode(roles)
print(encodedRoles == jsonData)  // "truen"
do {
    let decodedRoles = try JSONDecoder().decode([Role].self, from: jsonData)
    print(roles == decodedRoles)    // "truen"
} catch {
    print(error)
}
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